(1) Field of the Invention
The present invention relates to a semiconductor device in which thin film resistors made of bolometer materials are arranged in two-dimensional form corresponding to pixels. The present invention also relates to a trimming method performed in such a semiconductor device and a recording medium in which a program for executing the trimming is recorded.
(2) Description of the Prior Art
Semiconductor devices of this type include a thermal infrared imaging element, an infrared display apparatus, an ultrasonic sensor and the like in which the use of bolometer materials as a thin film resistor constituting part of a pixel or a sensor portion is typically known. For example, such devices include a thermal infrared imaging element which converts incident infrared rays into an electrical signal with a bolometer, an infrared display apparatus which provides a desired infrared image by supplying a bolometer with a predetermined bias voltage (or a bias current) to produce infrared rays (emit light), and the like. A configuration of such a thermal infrared imaging element is hereinafter described specifically as an example of the semiconductor device.
Each of Japanese Patent Laid-open. Publication No.8-105794 and Japanese Patent Laid-open Publication No.9-284651 discloses a thermal infrared imaging element comprising a plurality of thermoelectric converting elements arranged in matrix form which absorb and convert infrared rays radiated by respective portions of an object into heat which is converted into electrical signals for display as images. A pixel portion of the thermal infrared imaging element is shown in a sectional view in FIG. 1 and in a plan view in FIG. 2.
Referring to FIGS. 1 and 2, there is shown semiconductor substrate 20 on which scanning circuit 21 comprising a switch element and a shift register is formed, and silicon oxide film 22 partially including cavity 23 is formed on scanning circuit 21. A diaphragm (light receiving surface) defined by slit 26 is formed on cavity 23 in silicon oxide film 22. The diaphragm section has a three-layered configuration in which titanium bolometer 27, silicon oxide film 28, and titanium nitride 29 are sequentially stacked on silicon oxide film 22. On silicon oxide film 22, ground line 24, signal line 25, and vertical select line 30 which are made of aluminum (Al) are also formed. Signal line 25 is a vertical signal line and connected to titanium bolometer 27. Titanium bolometer 27, silicon oxide film 28, and titanium nitride 29 constituting the diaphragm are infrared absorbing layers in which the infrared rays reflected by titanium bolometer 27 is absorbed by titanium nitride 29. A plurality of scanning circuits 21 and a plurality of the diaphragms are integrated on semiconductor substrate 20 corresponding to pixels such that two-dimensional infrared images can be produced.
In the thermal infrared imaging element, when the infrared rays are incident on the diaphragm from above, the temperature of the diaphragm is changed and the electrical resistance value of titanium bolometer 27 is changed in accordance with the change in the temperature. The change in the resistance value of titanium bolometer 27 is electrically acquired through a read circuit and read to the outside as an infrared image.
FIG. 3 is a circuit diagram of the aforementioned thermal infrared imaging element. FIG. 4 is a timing chart for describing the operation of the thermal infrared imaging element.
As shown in FIG. 3, a pixel comprising bolometer 201 and vertical switch 202 is connected to vertical signal line 203 and further connected to horizontal switch 204. Four horizontal switches 204 are connected to one read circuit 206, and an output from each of read circuits 206 are sequentially provided through multiplexers 207 and output buffer 209 to the outside from output terminal 210. Read circuit 206 can be formed of an integrating circuit, a sample hold circuit, or the like, for example.
In the thermal infrared imaging element, as shown in FIG. 4, while an output (for example, V1) from vertical shift register 205 is at xe2x80x9cHxe2x80x9d level, vertical switches 202 connected thereto are turned ON and one of four horizontal switches 204 connected to read circuit 206 is turned ON, thereby selecting a pixel. According to this configuration, one vertical period can be divided into four such that a pixel can be selected for every four pixels in the horizontal direction. The detailed description of the operation is described in Japanese Patent Laid-open Publication No.8-105794 and Japanese Patent Laid-open Publication No.9-284651.
In the aforementioned conventional thermal infrared imaging element shown in FIG. 1 and FIG. 2, since titanium bolometer 27, ground line 24, and signal line 25 are disposed on the same substrate surface, some of a pixel area is occupied by ground line 24 and signal line 25, resulting in the problem of reducing the aperture rate (fill factor) for absorbing infrared rays.
Thus, for realizing an increased aperture rate, a thermal infrared imaging element with a three-dimensional structure is proposed in which lines such as a ground line and a signal line electrically connected to a read circuit are embedded in a layer under a diaphragm. An example of a thermal infrared imaging element with such a three-dimensional structure is hereinafter described.
FIG. 5 is a plan view of a pixel in a thermal infrared imaging element with a three-dimensional structure in which lines are embedded in a layer under a diaphragm, and FIG. 6 is a sectional view taken substantially along the lines X-Xxe2x80x2 of FIG. 5. Diaphragm 4 with air gap 2 disposed in a layer thereunder is supported by two beams 3 on Si substrate 1 provided with a read circuit. Diaphragm 4 comprises SiN insulating protective film 5, VOx bolometer material thin film 6 formed on protective film 5, SiN insulating protective film 7 formed on thin film 6 through SiO insulating protective film 8. Ti wire 11 surrounded by SiN insulating protective films 5, 7 and another insulating protective film 9 is formed to pass through two beams 3. Bolometer material thin film 6 within diaphragm 4 is connected to signal line 15 made of Al through Ti contact 12 and wire plug 13 made of tungsten, and signal line 15 is electrically connected to a read circuit within Si substrate 1. Total reflection film 14 made of Ti is disposed on a portion of a surface of Si substrate 1 provided with a read circuit that faces air gap 2.
In the thermal infrared imaging element, when infrared rays 10 are incident on diaphragm 4, the incident infrared rays are absorbed by SiN insulating protective film 5. Some of the infrared ray which cannot be absorbed by SiN insulating protective film 5 is reflected by total reflection film 14 toward diaphragm 4, and the reflected infrared rays are again absorbed by SiN insulating protective film 5. Since the line electrically connected to the read circuit is embedded in a layer under diaphragm 4, a pixel area is not occupied by the wire to allow an increased aperture rate for absorbing the infrared ray.
When the wire is embedded in the layer under the diaphragm as described above, a contact is typically provided for connecting each wire embedded in the lower layer to the bolometer in the diaphragm portion. FIG. 7 schematically shows a pixel arrangement and a positional relationship of contacts in a thermal infrared imaging element with wires embedded in a layer under a diaphragm. Ti contact 12A is a contact connected to a vertical signal line, and Ti contact 12B is a contact connected to a drain of a vertical switch constituting part of a pixel. In this configuration, the aperture rate can be further increased by reducing the size of each Ti contact and reducing a margin of the interval (interval between Ti contact 12A and Ti contact 12B in the lower right pixel) between Ti contacts in adjacent pixels.
However, it has been found from various analysis results previously made that an attempt to increase the aperture rate as described above develops pixel defects due to a contact short which causes deteriorated image quality. For example, in the pixel arrangement shown in FIG. 7, a reduced margin of the interval between Ti contacts produces a short in Ti contacts in adjacent pixels due to etching residues caused by the process, which deteriorates image quality. The problem of the contact short is described in detail next.
In the imaging element with the circuit configuration shown in FIG. 3, since one vertical period is divided into four such that a pixel is selected for every four pixels in the horizontal direction, more than one switches of four horizontal switches connected to one read circuit are not selected simultaneously. If a contact short occurs, however, a bias current to a bolometer also flows to an adjacent line through the short path.
FIG. 8 is a schematic diagram showing an example of a pixel arrangement in which a contact short occurs, FIG. 9 is a schematic circuit diagram including the contact short, and FIG. 10 is a schematic diagram showing resistance distribution including the contact short. In FIG. 8, each contact connected to a vertical signal line is represented as xe2x80x9cS,xe2x80x9d and each contact connected to a drain of a vertical switch is represented as xe2x80x9cD.xe2x80x9d FIG. 8 shows a state where a short occurs in S contact at row b and column 2 (hereinafter represented as [b,2]) and D contact at [c,3]. FIG. 9 illustrates the contact short shown in FIG. 8 in a circuit diagram, and FIG. 10 shows distribution of resistances of bolometers when the short path shown in FIG. 8 is produced. FIGS. 11a to 11c schematically show paths for flowing bias currents when the contact short shown in FIGS. 8 to 10 occurs. FIG. 11a shows a path for flowing a bias current when pixel [a,2] in FIG. 10 is selected, from which it can be seen that a bolometer resistance value is 2R/3. FIG. 11b shows a path for flowing a bias current when pixel [c,2] in FIG. 10 is selected, from which it can be seen that a short occurs. FIG. 11c shows a path for flowing a bias current when pixel [c,3] in FIG. 10 is selected, from which it can be seen that a bolometer resistance value is R.
In the thermal infrared imaging element, typically, variations in bolometer resistance values (unevenness) limit the dynamic range of the read circuit and produce variations in sensitivity of the imaging element. Thus, smaller variations (unevenness) are preferable in the bolometer resistance values. Evaluations in previously published papers show that variations (unevenness) in the bolometer resistance values are typically approximately 10% p-p with respect to the central resistance value, and a pixel with a resistance value above the range is a defective pixel. In the aforementioned three-dimensional configuration, assuming that the bolometer resistance value is R, the bolometer resistance value appears to be 2R/3 in two lines in the vertical direction where a contact short occurs, as shown in FIG. 10. This corresponds to xe2x88x9233% if converted into variations in resistance (unevenness), and the pixels with the two lines serve as defective pixels.
In this manner, a contact short at one point affects two lines in the vertical direction. For example, in an array of 320 by 240 in horizontal and vertical directions, respectively, if a contact short occurs at one point, the number of defects amounts to 480 pixels multiplied by 2 lines by 240 pixels, representing a deteriorated pixel defective rate. In addition, defective pixels due to such a contact short are produced regularly in two lines in the vertical direction, and are extremely prominent as linear flaws when imaging is performed, resulting in significantly deteriorated good item yields.
From the aforementioned reasons, in the imaging element with the three-dimensional configuration, a serious problem is how to eliminate deteriorated image quality due to a contact short for increasing the aperture rate. In addition, the problem of the deteriorated image quality due to a contact short described above occurs not only in the thermal infrared imaging element but also in general semiconductor devices including the aforementioned infrared display, ultrasonic sensor and the like.
It is an object of the present invention to provide a semiconductor device and a trimming method which can reduce the effect of defective pixels caused by the aforementioned contact short. It is another object of the present invention to provide a recording medium which records a program for executing the trimming.
To achieve the aforementioned objects, the semiconductor device of the present invention comprises thin film resistors arranged in two-dimensional form corresponding to pixels for converting incoming infrared rays into electrical signals or for emitting infrared rays, and selecting means for selecting an arbitrary thin film resistor to supply an overcurrent to the selected thin film resist.
The semiconductor device of the present invention comprises thin film resistors arranged in two-dimensional form corresponding to pixels for converting incoming infrared rays into electrical signals or for emitting infrared rays, wherein the thin film resistors are connected to a vertical signal line for each column and each of the thin film resistors is provided with a semiconductor switch, each of the pixels includes a first contact connected to the vertical signal line and a second contact connected to a drain of the semiconductor switch, and the first contact is disposed close to the second contact in adjacent pixels in the column direction.
The semiconductor device of the present invention comprises thin film resistors arranged in two-dimensional form corresponding to pixels for converting incoming infrared rays into electrical signals or for emitting infrared rays, wherein the thin film resistors are connected to a vertical signal line for each column and each of the thin film resistors is provided with a semiconductor switch, each of the pixels includes a first contact connected to the vertical signal line and a second contact connected to a drain of the semiconductor switch, and either the first contacts or the second contacts are disposed close to each other in adjacent pixels in the column direction. In this case, the first contact may be used in common for adjacent pixels in the column direction.
The trimming method of the present invention for a semiconductor device comprising thin film resistors arranged in two-dimensional form corresponding to pixels for converting incoming infrared rays into electrical signals or for emitting infrared rays comprises the step of flowing an overcurrent to desired thin film resistors.
The recording medium of the present invention records a program for causing a computer to execute the processing of:
sequentially selecting pixels in a semiconductor device comprising thin film resistors arranged in two-dimensional form corresponding to pixels for converting incoming infrared rays into electrical signals or for emitting infrared rays;
measuring resistance values of the thin film resistors of the selected pixels;
detecting a pixel with a resistance value deviating from a predefined value based on the measuring results; and
flowing an overcurrent to a thin film resistor in a predetermined pixel adjacent to the detected pixel.
In the present invention as described above, the following effects are provided.
As described in the aforementioned problem, when a contact short occurs in a pixel to be supplied with a bias current and a pixel adjacent thereto, the bias current also flows to an adjacent line through the short path to cause defective pixels in two lines in the vertical direction where the contact short occurs. According to the present invention, an overcurrent is supplied to a thin film resistor (bolometer) in the adjacent pixel where the contact short occurs. The thin film resistor (bolometer) supplied with the overcurrent is burnt by excessive self-heating, resulting in the elimination of the short path.
In an aspect of the present invention in which the first contact is disposed close to the second contact in adjacent pixels in the column direction, even when a contact short occurs, only the resistance value in the pixel including the second contact represents a short state and the effect is not produced on two lines in the vertical direction.
In an aspect of the present invention in which either first contacts or second contacts are disposed close to each other in adjacent pixels in the column direction, when a short occurs in the second contacts, its effect is produced only in the two pixels where the contact short occurs and the effect is not caused on two lines in the vertical direction. On the other hand, when a short occurs in the first contacts, the contact short causes no effect since they are connected to the same vertical signal line. In this configuration, in an aspect in which one of the contacts is used in common for adjacent pixels, the aperture rate and integration degree are further increased since wiring is also used in common.
The above and other objects, features, and advantages of the present invention will become apparent from the following description with reference to the accompanying drawings which illustrate examples of the present invention.